EMG amplitude, fatigue threshold, and time to task failure: A meta-analysis

Objectives Electromyographic (EMG) fatigue threshold (EMGFT) is utilised as a correlate of critical power, torque, and force thresholds that establishes a theoretical exercise intensity—the power, torque, or force at which the rate of change of EMG amplitude (ΔE M ¯ G) is zero—below which neuromuscular fatigue is negligible and unpredictable. Recent studies demonstrating neuromuscular fatigue below critical thresholds raise questions about the construct validity of EMGFT. The purpose of this analysis is to evaluate the construct validity of EMGFT by aggregating ΔE M ¯ G and time to task failure (Tlim) data. Design Meta-analysis. Methods Database search of MEDLINE, SPORTDiscus, Web of Science, and Cochrane (inception – September 2016) conducted using terms relevant to EMG and muscle fatigue. Inclusion criteria were studies reporting agonist muscle EMG amplitude data during constant force voluntary isometric contractions taken to task failure. Linear and nonlinear regression models were used to relate ΔE M ¯ G and Tlim data extracted from included studies. Results Regression analyses included data from 837 healthy adults from 43 studies. Relationships between ΔE M ¯ G and Tlim were strong in both nonlinear (R2 = 0.65) and linear (R2 = 0.82) models. ΔE M ¯ G at EMGFT was significantly nonzero overall and in 3 of 5 cohorts in the nonlinear model (p < 0.01) and in 2 of 5 cohorts in the linear model. Conclusions EMGFT lacks face validity as currently calculated; models for more precise EMGFT calculation are proposed. A new framework for prediction of task failure using EMG amplitude data alone is presented. The ΔE M ¯ G vs. Tlim relationship remains consistent across sexes and force vs. position tasks.